The present invention relates to a combined propulsion and steering system for a motor boat with an inboard engine.
At present, the propulsion system used for boats having a length up to about ten meters is usually a type known as a Z-transmission. This known transmission is very complex, however and also rather delicate, and requires careful handling and use.
On boats greater than about ten or twelve meters it is usual to employ a conventional submerged shaft. These have the disadvantage of being difficult to position, and they also have relatively high energy consumption which makes them expensive and, further, presents various disadvantages at high speed.
Attempts have been made to introduce propellers with so-called "surface" screws, that is screws which are not entirely submerged in normal use, but these attempts have lead to generally mediocre results as far as the overall performance is concerned; in particular the coefficients of acceleration have been inadequate and the performance at intermediate speeds has been generally unsatisfactory. Another disadvantage of surface screws lies in the fact that boats fitted with them generally have a poor manoevrability and considerable difficulty in reversing.